You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query>
    <pages>
      <page pageid="3" ns="0" title="Criando um Banco de Dados" />
      <page pageid="15" ns="0" title="Como acessar meus e-mails?" />
      <page pageid="18" ns="0" title="Criando contas de e-mail" />
      <page pageid="20" ns="0" title="Microsoft Outlook 2013" />
      <page pageid="29" ns="0" title="Como enviar meus arquivos pelo cPanel?" />
      <page pageid="35" ns="0" title="Onde coloco os meus arquivos?" />
    </pages>
  </query>
</api>